1. Field of the Invention
The present invention relates to parking devices for disk drives; more particularly, to devices which position and retain the head(s) of a disk drive over a selected portion of a hard (or fixed) disk when the disk drive is not in use.
2. Description of the Related Art
Developments in personal computers, portable computers and lap top computers have prompted reductions in the size and increases in the memory capacity of disk drives. Factors which hamper the incorporation and use of fixed or hard disks in lap-top computers include the size, weight, and power consumption of hard disk drives. The desire to operate portable computers on battery supplied power, and the reduction of the life of the batteries by each power consuming component of a computer, have prompted efforts to reduce the power consumed by disk drives intended for use in portable computers.
Conventional hard disk drives often incorporate a device for parking the head(s) of the drive. As used in this patent, the terms "park" and "parking" refer to the maintaining the position of the head(s) over a selected portion (usually a "landing zone" at the inside or outside diameter) of the disk (or disks). The heads are supported by an actuator, and parking the heads also means parking the actuator by fixing the position of the actuator which supports the heads.
In conventional disk drives, a head "flys" over the surface of a disk, riding on the stream of air created by the rotation of the disk. When the disk stops rotating, for example, when power is turned off, the head lands on the disk. If the head lands on a portion of the disk which is used to store data, there is a possibility that the disk, and thus the data stored on the disk, will be damaged. Parking the head(s) is particularly important in portable computers, in which the disk drive may be continually subject to large physical shocks during transportation. Non-operational physical shocks, for example, shocks experienced during transportation of portable computers or shipping may cause the heads to "slap" against the disk, possibly causing a loss of data if the head slaps against a data-carrying portion of the disk. Parking the head assures that the head will land on a landing zone--i.e., a non-data storage portion of the disk--and will be held in a position over the landing zone during the power-down period.
Various types of parking (or latching) devices have been used to lock the actuator arm of a voice coil in a selected position when the disk drive is not operating. Many parking devices incorporate a latch which physically engages the actuator arm and utilizes a sping to bias a pivoting latch arm to a parked position and an electromagnet to releast the latch during operation of the drive. The use of an electromagnet to release the latch requires the continual use of electrical power to maintain the latch in the unlatched position. Further, an electromagnet generates heat which is not desirable in a disk drive or any other area in a computer.
Air activated parking devices rely on the air flow generated by the rotating disks to release a spring biased latch arm. Air activated parking devices pose the problem of interference with the air flow necessary for the heads to fly properly. Further, the amount of force generated by the air flow is related to the surface area of the disks, and as disks are reduced in size, the amount of air flow may be insufficient to release a latch mechanism.
Solenoids have also been used to release latch arms which are spring biased. As with an electromagnet, a solenoid requires a constant supply of electrical current, and the residual magnetism of the plunger must be overcome by the biasing force.
Such parking devices often utilize pivoting latch arms which often present design, manufacturing, and operational problems related to, for example, balancing the latch arm to provide proper functioning of the latch for all orientations of the disk drive. A latch which does not operate properly for all orientations of the disk drive is not suitable for use in a portable or lap-top computer.
Reliability of electromagnetic parking devices which attract a permeable member requires overcoming any residual magnetism in the permeable member, prompting the use of larger bias springs. However, larger spring forces demand greater electrical power to energize an electromagnet which reliably overcomes the spring force.
Purely magnetic parking devices park the actuator by the attraction by a magnet of a magnetically permeable portion of the actuator. Such parking devices have provided direct contact between the magnetically permeable portion of the actuator and the magnet. The primary drawback of a magnetic latch of this type is that the rotational movement of the actuator is adversely affected by the attraction of the magnetically permeable portion of the actuator and the magnet, thereby creating problems with the track following and seek functions. Further, an extremely large force is required to release the actuator from the magnet.
Each component of a disk drive represents an increase in the weight of the drive, the space occupied by the drive, and the manufacturing effort. A large number of mechanical components, particularly the moving components of a latch mechanism, increases the possibility and probability of a mechanical failure of the drive. The number and complexity of mechanical components is also related to the ability of the drive to survive physical shocks and vibrations.